1. Field of the Invention
The present invention relates to a system for controlling transmission power from a base station in mobile communication and, more particularly, to a transmission power control system for controlling transmission power from a base station according to the change of a connection between a mobile station and a communication network in code division multiple access (CDMA) or other system mobile communication.
2. Description of the Related Art
In conventional time-division multiple access (TDMA) and analog mobile communication systems, a connection is established between a network and a mobile station through strictly one channel of one base station.
It is therefore possible to control transmission power of a channel connected by a base station itself based on a value of transmission power from the base station which is measured at and reported by a mobile station.
In addition, the conventional systems require transmission power control only for enabling a base station to maintain a connection with a mobile station and have no system problem as long as the control produces no effect on a reuse area of the same frequency.
Unlike conventional TDMA and analog systems, a code division multiple access (CDMA) mobile communication system has a connection mode called soft handoff (soft hand-over) in which a plurality of base stations and a plurality of channels connect with one mobile station.
In this soft handoff, to one mobile station coming to cell boundaries, an identification signal of a base station is sent out from a plurality of base stations. Then, when the mobile station fully enters any of the cells, switching of base stations (handoff or hand-over) is conducted.
A plurality of channels should therefore conduct transmission power control simultaneously. In addition, since a connection mode is changed every moment due to moving of a mobile station, control responsive to the change is required.
Moreover, a CDMA mobile communication system employs the same frequency for adjacent cells. No transmission power control, therefore, causes an interference wave to adjacent cells to reduce a traffic accommodation capacity of a cell and a traffic accommodation capacity of the system accordingly.
A first object of the present invention is to control transmission power from a base station at every call according to a connection state to improve a communication capacity in a CDMA mobile communication system.
Further and other objects, features and effects of the present invention will become apparent from detailed description in the following.
According to the first aspect of the invention, a transmission power control system for controlling, with a mobile station and two or more base stations simultaneously connectable to the mobile station, base stations and transmission power from the base stations to the mobile station, comprises
a control means for determining on a base station to be handed off based on information about a transmission strength of a pilot signal which each of the base stations transmits to the mobile station and information about a strength of the pilot signal received at the mobile station which is transmitted by the base station to control transmission power before and after handoff.
In the preferred construction, the control means comprises connection information holding means for grasping a base station being currently connected with the mobile station and storing the base station as connection information, control desired value obtaining means for obtaining information of a desired value of transmission power of the base station being currently connected, pilot signal obtaining means for obtaining transmission strength information of current the pilot signal of a base station which can be handed off by the mobile station, and simultaneous communication means for simultaneously transmitting handoff information which is information about handoff between the mobile station and each the base station to the currently connected base station and the base station which can be handed off.
In another preferred construction, the control means comprises connection information holding means for grasping a base station being currently connected with the mobile station and storing the base station as connection information, control desired value obtaining means for obtaining information of a desired value of transmission power of the base station being currently connected, pilot signal obtaining means for obtaining transmission strength information of current the pilot signal of a base station which can be handed off by the mobile station, and simultaneous communication means for simultaneously transmitting handoff information which is information about handoff between the mobile station and each the base station to the currently connected base station and the base station which can be handed off,
the simultaneous communication means transmitting communication channel number information which is information about the number of the base stations communicable with the mobile station before and after handoff as included in the handoff information.
According to the second aspect of the invention, a transmission power controlling method of controlling, with a mobile station and two or more base stations simultaneously connectable to the mobile station, base stations and transmission power from the base stations to the mobile station, comprising the steps of
determining on a base station to be handed off based on information about a transmission strength of a pilot signal which each of the base stations transmits to the mobile station and information about a strength of the pilot signal received at the mobile station which is transmitted by the base station, and
controlling transmission power before and after handoff.
In the preferred construction, the transmission power controlling method further comprising
a connection information holding step of grasping a base station being currently connected with the mobile station and storing the base station as connection information,
a control desired value obtaining step of obtaining information of a desired value of transmission power of the base station being currently connected,
a pilot signal obtaining step of obtaining information about a transmission strength of current the pilot signal of a base station which can be handed off by the mobile station, and
a simultaneous communication step of simultaneously transmitting handoff information which is information about handoff between the mobile station and each the base station to the currently connected base station and the base station which can be handed off.
In another preferred construction, the transmission power controlling method further comprising
a connection information holding step of grasping a base station being currently connected with the mobile station and storing the base station as connection information,
a control desired value obtaining step of obtaining information of a desired value of transmission power of the base station being currently connected,
a pilot signal obtaining step of obtaining information about a transmission strength of current the pilot signal of a base station which can be handed off by the mobile station, and
a simultaneous communication step of simultaneously transmitting handoff information which is information about handoff between the mobile station and each the base station to the currently connected base station and the base station which can be handed off, wherein
at the simultaneous communication step, communication channel number information which is information about the number of the base stations communicable with the mobile station before and after handoff is transmitted as included in the handoff information.
According to the third aspect of the invention, a computer readable memory which records a transmission power control program for controlling, with a mobile station and two or more base stations simultaneously connectable to the mobile station, base stations and transmission power from the base stations to the mobile station,
the transmission power control program comprising the steps of
determining on a base station to be handed off based on information about a transmission strength of a pilot signal which each of the base stations transmits to the mobile station and information about a strength of the pilot signal received at the mobile station which is transmitted by the base station, and
controlling transmission power before and after handoff.
According to another aspect of the invention, a transmission power control system for controlling, with a mobile station and two or more base stations simultaneously connectable to the mobile station, base stations and transmission power from the base stations to the mobile station, comprises
a controller which obtains information about a transmission strength of a pilot signal which each of the base stations transmits to the mobile station and information about a strength of the pilot signal received at the mobile station which is transmitted by the base station and determines on a base station to be handed off based on the transmission strength and the reception strength to control transmission power before and after handoff.
In the preferred construction, the controller comprises a connection information holding circuit which grasps a base station being currently connected with the mobile station and stores the base station as connection information, a control desired value obtaining circuit which obtains information of a desired value of transmission power of the base station being currently connected, a pilot signal obtaining circuit which obtains information about a transmission strength information of current the pilot signal of a base station which can be handed off by the mobile station, and a simultaneous communication circuit which simultaneously transmits handoff information which is information about handoff between the mobile station and each the base station to the currently connected base station and the base station which can be handed off.
In another preferred construction, the controller comprises a connection information holding circuit which grasps base station being currently connected with the mobile station and stores the base station as connection information, a control desired value obtaining circuit which obtains information of a desired value of transmission power of the base station being currently connected, a pilot signal obtaining circuit which obtains information about a transmission strength of current the pilot signal of a base station which can be handed off by the mobile station, and a simultaneous communication circuit which simultaneously transmits handoff information which is information about handoff between the mobile station and each the base station to the currently connected base station and the base station which can be handed off,
the simultaneous communication circuit transmits communication channel number information which is information about the number of the base stations communicable with the mobile station before and after handoff as included in the handoff information.
Other objects, features and advantages of the present invention will become clear from the detailed description given herebelow.